The present invention relates to a semiconductor device and, more particularly, to an improvement in such a device having wiring layers made of gold (called hereinafter "gold wiring layers").
Gold wiring layers have low sheet-resistivity and high reliability against the so-called electro-migration and stress-migration as compared to aluminum wiring layers. Accordingly, the gold wiring layers have become essential to such a semiconductor device that is required to operate at a very high speed and to drive a load circuit with a large current. However, gold in the gold wiring layer is easy to diffuse into an element region to thereby destroy a junction of the element region. A barrier metal layer is therefore provided between the gold wiring layer and the element region.
Referring to FIG. 5, a semiconductor device according to a prior art includes an N-type diffusion 13 region as the element region, which is selectively formed in a P-type substrate 1. Formed on the substrate 1 is an inorganic insulating film 3a which in turn has a contact hole 2 to expose a part of the diffusion region 13. A platinum-silicide layer 10 is formed at the exposed part of the diffusion region 13 to reduce a contact resistance. A plurality of gold wiring layers 4a-7a at a first-level in a multi-level wiring structure (i.e., a plurality of first-level gold wiring layers) are formed on the insulating film 3a. The gold layer 7a is provided as a current path to form the gold layer 4a by the plating method. The right-hand wiring layer 4a-7a is connected to the diffusion region 13 through the contact hole 2. As mentioned hereinbefore, a barrier layer 5a made of titanium-tungsten alloy is formed between the gold wiring layer 4a-7a and the silicide layer 10.
This device further includes an inter-layer insulating layer formed over the entire surface, which is composed of an inorganic insulating film 3b, an inorganic spin-on insulating film 8a, an inorganic insulating film 3c and an inorganic spin-on insulating film 8b formed in that order. The spin-on insulating film 8a and 8b are provided to fill hollows to even out the inter-layer insulating layer. A contact hole 9 is selectively formed in the inter-layer insulating film to expose a part of the left-hand gold wiring layer 4a-7a. The left-hand wiring layer is thus connected via the contact hole 9 to a gold wiring layer 4b-7b at a second level in the multi-level wiring structure (i.e., a second-level gold wiring layer). Similarly to the first-level wiring layer, the gold layer 7b serves as a current path to form the gold layer 4b by the plating method, and a barrier metal layer 5c made of titanium-tungsten alloy. An inorganic insulating film 3e is formed on the second-level wiring layer to protect the surface thereof.
Turning to FIGS. 6 and 7, there are illustrated semiconductor devices according to other prior arts, in which the same constituents as those shown in FIG. 5 are denoted by the same reference numerals to omit further description thereof. In these devices, a platinum layer 6b and a palladium layer 12b are employed as a current path for forming the gold layers 4a and 4b by the plating method.
Referring to FIG. 8, a semiconductor device according to still another prior art employs tungsten layers 11a and 11b to fill the contact holes 2 and 9, respectively. The remaining constituents are the same as those shown in FIG. 5 and therefore the description thereof is omitted.
Thus, various types of semiconductor devices having the gold wiring layers are proposed or put into practical use; however, each of such devices has a drawback indicated below:
In the device shown in FIG. 5, although titanium in the alloy layer 5a diffuses into the gold layer 4a and then appears on the surface of thereof to thereby enhance the adhesion between the gold wiring layer 4a and the inter-layer insulating layer, the titanium-tungsten layer 5a has an insufficient barrier effect against gold. For this reason, gold in the gold wiring layer 4a-7a may diffuse into the region 13 through the barrier layer 5a in the heat treatment at about 400.degree. C. for enhancing the so-called ohmic contact, so that the PN junction between the region 13 and substrate 1 is finally destroyed.
In the device shown in FIG. 6, on the other hand, the platinum layer 6b formed on the titanium-tungsten layer 5a has a superior barrier effect against gold to prevent gold from diffusing into the region 13. However, platinum in the layer 6b in turn diffuses into the gold layer 4a and moreover the platinum layer 6b prevents titanium form diffusing into the gold layer 4a. For this reason, the adhesion between the gold layer 4a and the inter-layer insulating layer is deteriorated as compared to the device of FIG. 1. Similar drawback occurs in the device shown in FIG. 7, since the palladium layer 12b is substantially equal in characteristics to the platinum layer 6b.
In the device shown in FIG. 8, the tungsten layer 11a has an insufficient barrier effect against gold, similarly to the titanium layer.